1. Field of the Invention
The present invention relates to a method and apparatus for efficiently operating a network, and more particularly, to a method and apparatus for efficiently performing discovery of a maximum transmission unit (MTU) on a path of a network.
2. Description of the Related Art
As the number of Internet users has been rapidly increasing recently, the 32-bit address system in the networks based on the related art Internet Protocol version 4 (IPv4) has shown the limits of Internet protocol (IP) addresses and functional restrictions. To solve these problems, related art Internet Protocol version 6 (IPv6), by which a variety of services can be provided through diverse expanded functions with a 128-bit address system, has been proposed.
In the related art IPv4, when the size of a packet is greater than a link MTU, a router located on a routing path performs fragmentation of the packet. However, in the IPv6 (unlike in the IPv4), if a packet is transmitted by a source node, a node in the middle of a path does not perform fragmentation of the packet. Instead, the source node searches for a minimum MTU on a path, fragments packets according to the discovered MTU, and transmits fragmented packets.
Accordingly, when an IPv6 node, that is, a source node, is desired to transmit data to a destination node in a remote location, a link MTU of a path through which a packet is transmitted is first discovered. That is, a path MTU (hereinafter referred to as “PMTU”) that is a minimum link MTU in a routing path between the source node and the destination node should be determined.
According to the related art PMTU discovery method, when a source node first transmits a packet, the source node fragments the packet in units each having the size of a next-hop link MTU, and transmits the fragmented packet.
When the size of a packet transmitted from the source node is greater than a link MTU between hops in the routing path, this packet is discarded, and an Internet Control Message Protocol (ICMP)-Packet Too Big message containing next-hop link MTU information is generated and transmitted to the source node. Using the MTU information of the ICMP-Packet Too Big message, the source node fragments the packet again, and transmits it again. The aforementioned related art routine is repeated until the packet arrives at the destination node without being discarded after being transmitted by the source node.
FIG. 1 is a diagram showing a process of PMTU discovery by using the related art PMTU discovery method when the link MTU between a source node 110 and a destination node 150 decreases in the order of 6, 5, 4, and 3.
First, a source node 110 generates a packet {circle around (1)} (MTU=6) based on the MTU value 6 to the next node, a first node 120, and transmits the packet to the first node 120. Since the size of the received packet {circle around (1)} (MTU=6) is greater than the next-hop link MTU value 5, a first node 120 discards the received packet {circle around (1)} (MTU=6), and generates an ICMP error message containing next-hop link MTU information, which is MTU=5. That is, the first node 120 generates an ICMP Packet Too Big message {circle around (2)} (MTU=5), and transmits the message to the source node 110.
The source node 110 fragments the packet again according to the next-hop link MTU value, that is, MTU=5, of the first node 120 contained in the received ICMP Packet Too Big message {circle around (2)} (MTU=5) transmitted by the first node 120, and transmits the re-fragmented packet {circle around (3)} (MTU=5) to the destination node 150.
Since the size of the received packet {circle around (3)} (MTU=5) is greater than the next-hop link MTU value, that is, MTU=4, a second node 130 discards the received packet {circle around (3)} (MTU=5), generates an ICMP error message {circle around (4)} (MTU=4) containing the next-hop link MTU information, and transmits the message to the source node 110. As in the previous step, the source node 110 fragments the packet to satisfy the new link MTU=4, and transmits the fragmented packet {circle around (5)} (MTU=4) to the destination node 150.
As in the first and second nodes, since the size of the received packet {circle around (5)} (MTU=4) is greater than the next-hop link MTU value, that is, MTU=3, a third node 140 discards the received packet {circle around (5)} (MTU=4), generates an ICMP error message {circle around (6)} (MTU=3) containing the next-hop link MTU information, and transmits the message to the source node 110. As in the previous step, the source node 110 fragments the packet to satisfy the new link MTU, and transmits the fragmented packet {circle around (7)} (MTU=3) to the destination node 150.
The related art scheme has various problems and disadvantages. For example, but not by way of limitation, in the related art PMTU discovery method, in order to discover a PMTU between the source node and destination node, much time is spent (e.g., performing fragmentation) and network resources are unnecessarily wasted.